Swapping 4.56 to 3.73 or maybe 4.10
 

I run my 78 K20 stock. I carry lumber/tools in the bed, but I rarely/never tow. I have 4.56 gearing in the rear. I get terrible gas milage. Has anyone swapped to a 4.10? How much better was your milage? I know my GM 10.5" 14 bolt only came in 4.10 or 4.56 originally. Can you go down to a 3.73? Thanks!

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

What size tires are you running?

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

265/75R16. Pretty close to the stock size.

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

For the 20/30 series trucks w/16" rims (assuming close to stock tires) IMHO 4.10's are the best all-purpose ratio. On my '85 with stock 454/TH400/4.10's, the only reason I'd go down to 3.73's is if I was going to use it primarily for highway towing. Otherwise, 4.10's are a good compromise providing adequate RPM's to accelerate and climb hills in <55 MPH speed limits, but keeping RPM's below 3,000 until around 70 MPH.

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

4L80E or gear vendors swap? Makes a 4.56 into a 3.32. Although you can pay for a lot of gas for the cost. Jay

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

That would be a lot of miles to justify the cost of a gear swap. If it is truly that big of an issue I'd buy bigger tires instead.

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

My 81 factory light 3/4 ton has 3.43's with no overdrive. My 99 weighs 5600# with me and no gas and has 3.43's with OD, running LT235/16/r78's. With an overdrive trans and a v8, 3.73's would probably be better. You can get away with less gears with a V8 and an auto due to torque multiplication in the converter for starting the load.

Best bet is to pick your tire and trans, then use an online calculator to find the gear. I like to run my stuff 17-1800 at 60mph, puts 72 right around 2000 rpm which should be in the good part of the torque curve. I don't tow a ton (mostly DD) and when I do I run in 3rd gear and keep the speeds low.

Re: Swapping 4.56 to 3.73 or maybe 4.10
 

IMHO, 3.73 would be fine for what you do. I have 4.10 in my CC dually and really wish I had an overdrive on the freeway. For around town it is even a bit steep. I think I would be happy with 3.73 for 95% of what I do. I would be happiest with 4.10 and overdrive.